The US government has set a goal of freeing up 500 MHz of spectrum for wireless communication. A large portion of this will come from incumbents. Accordingly, dynamic spectrum access (DSA) will be beneficial to harnessing the new spectrum. DSA networking involves discovering available channels for DSA devices to communicate at a particular time and location. Currently, there are two expected approaches: one is to query a geo-location database to obtain information on unoccupied channels in a particular location; and the other is to let DSA devices sense/search a wide band of radio frequency and find unused channels.
Most prior work on wide band spectrum sensing can be classified into two types: sequential scan and wideband scan. Both performed in the digital domain. Sequential scan requires only a narrow-band radio, but is very slow if there are hundreds or thousands of channels since each channel is scanned in sequence. Since each scan on one channel may take several msec to several hundreds of msec, it could easily take tens of seconds to find all available channels. Wideband scan uses a wideband radio with high speed analog-to-digital converters (ADCs). A wideband radio is expensive and also very power consuming. Not only does the high speed ADC consumes significant power, but also more computations are needed to process the large amount of samples that leads to a higher power cost. Such price and power costs make sensing at the Nyquist sampling rate prohibitive to mobile devices.